Succinic acid and its derivatives are widely used as a specialty chemical for applications in polymers, foods, pharmaceuticals, and cosmetics. Furthermore, succinic acid is a valuable 4-carbon intermediate useful for the production of 1,4-butanediol, tetrahydrofuran, and gammabutyrolactone.
Although the succinate ion is a common intermediate in the metabolic pathway of several anaerobic microorganisms, there are no published examples of any fermentation that produces succinate in large amounts or with high yields. For example, succinate is a key intermediate for anaerobic fermentations by propionate-producing bacteria, but it is only produced in low yields and in low concentrations.
Succinate is also produced by anaerobic rumen bacteria These bacteria include Bacteroides ruminicola whose growth and metabolism is described by Howlett et al. (1976) and Bacteroides amylophilus whose culture and growth are described by Caldwell et al. J. Bacteriol., 98, 668-76 (1969) and Hamlin et al. J. Bacteriol., 72, 548-54 (1956).
Although the rumen bacteria give higher yields of succinate than do the propionate-producing bacteria, the reported fermentations were run in very dilute solutions and gave a variety of products in generally low yields. Moreover, the rumen organisms tend to lyse after a comparatively short fermentation time, thereby leading to unstable fermentations.
Anderson and Ordal described in J. Bacteriol., 81, 139 (1969) the isolation of a facultative anaerobe, Cytophaga succinicans, which produced succinate, acetate, and formate from dextrose with fixation of carbon dioxide. However, this organism produced succinate in such low concentrations that it would not be economically feasible to recover succinic acid from the fermentation medium. Similar results were observed with the Bacteriodes fragilis obtained from the gastrointestinal tract (Caspari et al., Arch. Microbiol., 135, 16-24 (1983).
In order to develop a commercially attractive process to produce succinic acid by fermentation, several important fermentation and product purification criteria need to be accomplished. The fermentation should be high yield (wt %) and produce a high product concentration using inexpensive raw materials and nutrients. Since anaerobic fermentations are run at neutral or near neutral pHs, salts of organic acids rather than the acids themselves are produced. The fermentation broth also contains cells, protein and other undesirable materials. The desired product from the process is the purified acid which can be used for specialty or commodity chemical manufacture. Hence, to be commercially viable, a high yielding, economical fermentation process has to be integrated with an efficient recovery and purification process.
We have previously demonstrated that Anaerobiospirillum succiniciproducens (ATCC 53488) produces enough succinate to allow simultaneous fermentation and calcium succinate precipitation under strictly controlled conditions and when the correct calcium salt is used for neutralization. However, for an economic process, the fermentation should use low cost nutrients, have high yield, high productivity, recycle nutrients and the recovery of the precipitated calcium succinate. Furthermore, the recovery of dissolved succinate from the filtrate is desirable. In addition, the succinate obtained must then be economically converted to high purity succinic acid.